"His Highness has arrived back in Thailand from Germany and will attend an event this evening at the 1st Infantry Regiment, King's Own Guards. This is confirmed," said a senior military source who declined to be named because of the sensitivity of the matter.

The prince's return to Thailand, will likely ease any concerns about the succession, said Bangkok-based lecturer and analyst Gothom Arya.

"His return will likely stop any lingering rumours that the ascension process, when it happens, will not proceed smoothly," he told Reuters.

The prince has spent much of his adult life abroad, and has a home in Germany where his son, Prince Dipangkorn, is enrolled at a private school.

Thailand's military government submitted a new constitution for royal endorsement on Tuesday. Prayuth Chan-ocha has said that only the new monarch can approve the charter.

By law, the monarch or regent, has 90 days to approve the constitution after it is submitted.